Ormocer coated papermachine clothing

ABSTRACT

A method of coating an ormocer (organically modified ceramic) on a papermachine clothing.

The present invention relates to phase separation apparatus for use inphase separation processes, including papermaking and filtration.

When carrying out a phase separation process it is generally importantto use phase separation media that exhibit good abrasion resistance,cleanliness and stability.

It is an object of the present invention to provide phase separationapparatus which exhibit such properties.

According to the present invention there is provided the use of at leastone ormocer in phase separation apparatus.

The ormocer preferably acts as a phase separation medium such as afilter or papermachine clothing.

The phase separation apparatus of the invention may comprisepapermachine clothing possibly including a fabric in combination withthe ormocer.

Alternatively the phase separation apparatus may comprise a filtercomprising a filter element including the ormocer.

Ormocers (organically-modified ceramics) are inorganic/organiccomposites combining the properties of ceramics with those of organiccomponents. For the avoidance of doubt the term ormocer used hereinincludes organically-modified silicates. One example of an ormocer is anorganosilane-impregnated silica gel which can be pyrolysed to formSiC-reinforced silica which is two to three times harder than the silicamatrix alone.

An ormocer typically comprises a polar component, a hydrophobiccomponent and micro-ceramic particles. The polar component provides goodadhesion of the ormocer to the substrate. This is particularly importantfor papermachine clothing where adhesion of coatings to conventionalpolyethylene terephthalate (PET) clothing material is difficult toachieve. The hydrophobic component, which may be a fluorinated material,is preferably orientated to the air-coating interface so as to impartnon-stick properties at the coating surface. The micro-ceramic particlesimpart abrasion resistance and anti-scratch properties.

The ormocers can be made by a typical sol-gel process. Gels are usefulin that they have a good capacity to incorporate both organic andinorganic components and they allow very fine ormocer particles to beproduced. Generally, sol-gel derived materials can be cast to shape atroom temperature. Therefore they are excellent low-temperature hosts fororganic molecules, polymers and fibres.

An additional method of preparing an ormocer coating is by impregnatingporous xerogels with organic monomers and then curing the coating insitu.

Ormosils can be made by combining tetraalkoxysilanes with alkylsubstituted and organofunctional alkoxysilanes, namely Si(OR)₄ +R₂Si(OR)₂ +YR¹ Si(OR)₃ where R is alkyl, R¹ is alkylenyl and Y is anorganofunctional group such as --R¹ --NH₂, --R¹ NHCOONH₂ or --R¹ --S--R¹--CHO. The choice of precursors depends on the solubility or thermalstability of the organofunctional substituents.

Typically ormocers are based on alumina, zirconia, titanium dioxide orsilica-based organic network formers containing epoxy or methacrylategroups bonded to silicon atoms via a Si--C bond.

Either the network formers or work modifiers can be tailored forspecific applications. For example, epoxysilanes may be used to impartscratch resistance. Thermoplastic or photocurable groups based ondiphenylsilanes or photocurable ligands, such as methacryl vinyl orallyl groups, in combination with a variety of polymerisable monomersmay be used for coatings and adhesiveness.

The ormocer may be coated on a surface of a substrate. The substrate maycomprise ceramic, glass, metal or plastics, but is preferably a fabric.Any suitable coating method may be employed for coating the substratewith the ormocer, such as immersion, spraying or roller or lick coating.The ormocer is then heated to a temperature in the order of 90° C. to140° C. depending on the ormocer concerned, or is cured by ultra-violetradiation (eg wave lengths of 365 nm or 254 nm) to fix the ormocer ontothe substrate. Adherence of the coating to a PET substrate may beimproved by pretreatment of the substrate by means of a primer or coronadischarge.

Alternatively, if the substrate is a fabric, the individual yarns may beindividually coated with the ormocer prior to their incorporation intothe fabric. Otherwise finely divided ormocer particles may be introducedinto the polymer melt prior to extrusion. The constituent polymer yarnsof the fabric may be extruded in this manner.

When used in papermachine clothing such as forming wires or dryerfabrics the hydrophobic nature of the ormocer coating reduces theaccumulation of pitch and other contaminants in the fabric. The fabricstability, particularly for forming fabrics is improved by the fixing ofyarn cross-over points. In addition the coatings are highly heatresistant and far more resistant to water vapour penetration thanconventional coatings comprising purely organic materials. The ceramicnature of the coating may advantageously be used in fabrics in the fieldof impulse drying by offering protection against glazing.

Applications in the field of filtration include ultra-filters (finefilter elements). These are generally prepared from ceramics in order toachieve resistance to corrosion and high temperatures. Sol-geltechnology enables ultra-filters with a 1-100 nm diameter pore size tobe prepared on, for example a porous or (semi) flexible substrate, suchas a filter fabric.

In a further embodiment of the invention the phase separation apparatuscomprises a papermaking machine, calender machine or the like using aroller, at least a part of the roller having a coating comprising theormocer.

The invention has particular application in rollers in the press anddryer sections of papermaking machines, and off-machine calender rolls.

Known calender rolls are often made of many cotton, steel or syntheticdiscs arranged on a mandrel which are then optionally coated with resinand/or polymer. The calender rolls are subject to abrasion when in use.Known cotton rolls generally exhibit poor releasability.

The ormocer coated rollers of the invention show vastly improvedabrasion resistance and releasability. Releasability can be improved bythe incorporation of a fluoropolymer into the coating. This isespecially useful for rollers used in the preparation of resin-treatedfabrics.

Furthermore any damaged area of coating could be easily repaired bystripping a patch around the damaged area, for example by sandblastingand then simply applying a fresh coating of ormocer to the strippedarea.

The ormocers used in the phase separation apparatus of the presentinvention are preferably based upon polycondensates of one or morehydrolysable compounds of elements of main groups III to V andsub-groups II to IV of the periodic table, such as boron, aluminium,silicon, tin, lead, titanium, zirconium, vanadium or zinc. Thehydrolysable compounds ideally contain hydrolysable groups andnon-hydrolysable carbon-containing groups in a molar ratio from 10-1 to1-2 with respect to the monomeric starting materials. At least some ofthe non-hydrolysable carbon-containing groups ideally comprise fluorineatoms bonded to carbon atoms.

The compounds are made by mixing the required starting materialstogether in water for hydrolysis and precondensation. Any fluorinecontaining materials are, however, added after hydrolysis andprecondensation of the other materials. After the fluorinated groupshave reacted with the other materials more water may be added. Thismethod prevents the fluorinated materials separating out from the othermaterials so as to provide a two-phase system.

The hydrolysable groups referred to above preferably comprise one ormore of the following: alkoxy, aryloxy, acyloxy, alkylcarbonyl halogenor hydrogen.

The non-hydrolysable groups referred to above preferably comprise one ormore of the following: alkyl, alkenyl, alkynyl, aryl, alkaryl or alkoxy.

Examples of suitable starting materials include any of the following:##STR1##

In order that the present invention may be more readily understood aspecific embodiment thereof will now be described by way of exampleonly:

A typical ormocer coating for papermachine clothing was prepared byhydrolysing gamma-glycidyloxypropyltrimethoxysilane (using 1.5 moles ofwater per mole of the silane) at pH 5.5 (obtained by bubbling withcarbon dioxide) for 16 hours at 25° C. This hydrolysed silane wasapplied to a PET fabric by dip coating and then cured at 130° C.

The 10 micron thick coating remained undamaged after 14 days at 40° C.,100% relative humidity and showed good adhesion, flexibility andabrasion resistance.

It is to be understood that the above described embodiment is by way ofillustration only. Many modifications and variations are possible.

We claim:
 1. A method of using at least one ormocer as coating forfacilitating phase separation in a papermachine clothing, consistingessentially of:providing at least one ormocer; and coating thepapermachine clothing with the at least one ormocer, wherein the ormocercomprises a perfluorinated material.
 2. The method as claimed in claim1, wherein the paperclothing machine is selected from the groupconsisting of yarn and fabric.
 3. The method as claimed in claim 2,wherein the ormocer comprises a polar component, a hydrophobic componentand micro-ceramic particles, the polar component being orientatedtowards the substrate and the hydrophobic component being orientatedtowards